In order to prevent environmental pollution caused by the volatilization of organic solvents, in the field of coating compositions for coating the inner surfaces of cans, such as food cans, aqueous coating compositions are gradually replacing organic solvent-based coating compositions. As aqueous coating compositions, Japanese Examined Patent Publication No. 1988-41934 and Japanese Unexamined Patent Publication No. 1995-138523 propose acrylic-modified epoxy resin based aqueous coating compositions that are obtained by reacting or mixing epoxy resins and carboxyl-containing acrylic resins.
However, in order to obtain a coating film with satisfactory coatability and excellent properties, in the aqueous coating compositions heretofore used, a high-molecular-weight epoxy resin obtained by reacting a low-molecular-weight bisphenol A epoxy resin with bisphenol A is generally used as the starting epoxy resin. Therefore, some portion of bisphenol A remains in the coating composition unreacted. However, bisphenol A is one of the chemicals has recently been identified as a possible environmental hormone, which has led to a strong demand for the development of a coating composition that is free from bisphenol A leaching.